Methodological note on patchy reionization and anisotropic cosmic birefringence
I wrote a methodological note on how to interpret anisotropic cosmic birefringence constraints when an effective contribution from patchy reionization is present.
The note emphasizes that current anisotropic cosmic birefringence constraints should be read as constraints on the total birefringence power, rather than automatically as limits on a single ALP-induced fluctuation component. It also documents why finite-width visibility averaging is essential: thin-shell estimates can make the patchy contribution look more important than it remains after a more physical treatment.
The full note is available on GitHub: